Nucleotide metabolism in cardiac activity. II. Reactions in systole

Relaxed mammalian hearts contain ATP as the predominant nucleotide, sometimes accompanied by smaller amounts of ADP, presumably formed during manipulation. In systole, one-tenth of the nucleotide is changed into a new compound, nucleotide H.

The effect of exercise on coronary blood flow, myocardial oxygen consumption and cardiac efficiency in man

It has been known that exercise causes an increase in the coronary blood flow in animals. The present work has been carried out to study the effect of exercise on coronary blood flow and myocardial oxygen consumption of the human heart in vivo. The results indicate that the heart responds to the increased load of exercise with a rise in coronary blood flow. Since the arteriovenous coronary oxygen difference shows little change, the increase in oxygen consumption of the heart muscle is primarily the result of an increased coronary blood flow. As the cardiac work rises more than the myocardial oxygen consumption, the left ventricular efficiency increases. The response of the failing heart muscle to acute increases in load produced by exercise does not differ from that of the normal heart or of the isolated heart.

Nucleotide metabolism in cardiac activity. I. Methods

The application of ion-exchange chromatography for the determination of adenosine nucleotides in mammalian hearts is described. It is found that 1 gram ventricular muscle contains nearly 5 x 10 -6 mole of adenine nucleotides, presumably present as ATP in the relaxed heart in vivo. After isolation of the heart, breakdown of ATP takes place especially under anaerobic conditions, and the reaction products AMP and IMP diffuse into the medium. Effects upon these reactions of glucose, glutamic acid and excess potassium are suggested by preliminary experiments.